New Delhi, Dec. 22 -- At some point, almost everyone has tried it. Your phone battery is dying and the phone charger is missing but the laptop charger is right there. Same USB-C port. Same cable. You plug it in and wait, half expecting something to go wrong. Most of the time, nothing does. The phone charges. Slowly or quickly, it depends. What looks like a lucky coincidence is actually the result of years of standardisation around USB-C and power negotiation. That promise of one charger for everything was never make-believe, it just came with fine print.

USB-C is not just a connector. It is backed by a system called USB Power Delivery. This is what allows devices to talk to each other before power flows. The charger does not blindly push...